Methionine and 2-hydroxy-4-(methylthio)butanoic acid (which may hereinafter also be referred to as “liquid methionine”) are both useful as an additive for animal feed. Methionine and liquid methionine are produced by using 3-(methylthio)propionaldehyde as a raw material.
As a method for producing methionine, for example, Patent Document 1 discloses a method for obtaining methionine, the method comprising obtaining 2-hydroxy-4-(methylthio)butanenitrile by reacting 3-(methylthio)propionaldehyde with hydrogen cyanide in the presence of a base, then reacting the resulting 2-hydroxy-4-(methylthio)butanenitrile with ammonium carbonate to give 5-(β-methylmercaptoethyl)hydantoin, followed by hydrolysis in the presence of a basic potassium compound to obtain methionine.
Patent Document 2 discloses a method for producing methionine at a high yield, the method comprising obtaining 2-amino-4-(methylthio)butanenitrile by reacting 3-(methylthio)propionaldehyde, hydrogen cyanide, and ammonia, and contacting the obtained 2-amino-4-(methylthio)butanenitrile with water in the presence of an oxide catalyst containing cerium.
As a method for producing liquid methionine, for example, Patent Document 3 discloses a method for obtaining liquid methionine, the method comprising reacting 3-(methylthio)propionaldehyde with hydrogen cyanide, followed by hydrolysis of the resulting 2-hydroxy-4-(methylthio)butanenitrile in the presence of sulfuric acid.